Fugacity of a Single Component: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Fugacity is an intensive variable, so it does not depend on the amount of the phase.
  • Fugacity is the driving force for mass transfer, not concentration.
  • The fugacity for a single-component ideal gas is equal to its pressure.
  • The fugacity for a single-component liquid is equal to its saturation pressure if pressure is low enough that the gas phase is ideal.
  • The fugacity of a single-component, non-ideal gas is less than its pressure and approaches the pressure as the temperature increases.
  • When phases are in equilibrium for a single-component, the fugacity of that component is the same in each phase.
  • Mass transfer is not always from the phase with the higher concentration to the phase with the lower concentration.
  • The fugacity of a liquid or solid does not change much as pressure increases.
  • As the temperature of a pure liquid increases, its fugacity increases.
  • As the temperature of an ideal gas increases at constant pressure, its fugacity does not change.
  • As the pressure of a pure component increases, its fugacity increases, but the increase will be much smaller for a liquid or solid than a gas.
From studying this module, you should now be able to:
  • Calculate fugacity of a single-component ideal gas.
  • Calculate the fugacity of a liquid or a solid.
  • Calculate the fugacity of a non-ideal gas.
  • Determine the direction of mass transfer between phases.
  • Calculate the fugacity of a liquid or solid at high pressure using the Poynting correction.
  • Explain the criteria for single-component phase equilibrium in terms of fugacity.
  • Explain why the fugacity of a saturated liquid is close to the vapor pressure of the liquid.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder